The present invention relates in general to electric heating blankets, pads, pillows and the like and in particular to such heating products which include internal strips of heat reflective material.
Present day warning blankets can draw as much as 180 watts of power during normal operation. Reducing this power is desirable for several reasons. First, reducing the power saves energy and makes the blanket more economical to operate. Second, reducing the wattage offers the possibility of reducing the size of the wire which lowers cost and improves comfort. Third, controlling a reduced wattage blanket allows the control electronics to dissipate less heat thereby allowing for the use of a smaller heat sink. Finally, by using less power, the operating voltage can be reduced to, say, about 33 volts AC which is less complicated to operate and poses fewer safety issues.
Unfortunately, if one just decreases the wattage of a heating blanket, the blanket will not produce sufficient heat for a user. In order to allow the wattage to be decreased and yet provide the same amount of heat to a user, the heat losses from the blanket must also be decreased. Attempting to insulate the blanket to reduce heat losses doesn""t solve the problem. By insulating the blanket, the heat losses are reduced, but then it is also more difficult for the heat to flow through the insulation from the wire to the user. Using a heat reflective sheet can help, but such sheets are bulky and prevent the blanket from breathing, i.e., from allowing water vapor to flow outwardly from a user""s body through the blanket.
What is required is some way to prevent heat losses without impeding the flow of heat from the wires to the user and without significantly affecting the passage of moisture or breatheability of the blanket. The solution, according to this invention, is to place strips of thermally reflective material on the top side of the blanket and aligned over the heating wires. In this manner substantially all of the available heat is directed downward towards the user, thereby increasing the amount of heat delivered to the user for a given input wattage, or allowing for the use of a lower wattage input with equivalent heating.
The present invention has been developed to fulfill the needs noted above and therefore has as an object the provision of a heating blanket, pad, pillow or the like which provides (transfers) equivalent heat to a user as that provided by similar conventional heating products, yet which requires significantly less electrical power to achieve such equivalent warming.
This result is achieved by providing a heat reflective layer of material in the form of thin heat reflecting strips or bands on only one side of the heating elements, which are typically resistance wires. The reflective layer can be provided as thin strips of heat reflective metal or plastic foil sewn or bonded onto the blanket or onto a substrate within the blanket. Aluminized coatings can also be used as well as titanium compounds such as found on ironing board covers. The thin strips are aligned directly over the top surface of the resistance wires to reflect heat downwardly to a user.
The strips can also be applied as a spray or liquid coating to the blanket or to an internal substrate within the blanket. The spray can be applied by a moving nozzle in the manner of applying spray paint or applied over a stencil with a spray nozzle, brush or roller.
Another approach is to apply a reflective coating directly to a portion, i.e., the upper half, of the resistance wire. The reflective coating or strips can also be applied as heat reflective adhesive tape. In each of the noted variations, substantially all of the heat produced by the resistance wire is transferred to a user, thereby increasing the amount of heat transferred to the user for a given input wattage to the heating wires or heating elements.
By limiting the heat reflective material to thin bands, thin coatings or thin patches or strips located directly above the heating element (wires), most of the blanket remains xe2x80x9cbreathable,xe2x80x9d i.e., capable of passing moisture, i.e., water vapor, outwardly to the ambient from a user. This greatly improves the comfort of the user and allows the blanket to remain lightweight, pliable and compliant.
In order to construct the reduced wattage blanket, heating wire is first laid out on a thin pliable substrate. Then strips of the thermally reflective material are placed over the wires. The reflective material is then attached to the substrate, and can also secure the wire to the substrate. Finally, the complete substrate is placed inside a blanket shell. It is also possible to eliminate the substrate and apply the wire directly to an interior surface of the upper half of the shell, preferably before the two halves of the shell are completely sewn together.